Influence of demixing on SF6 arc properties

Experimental analyses of wall stabilized SF6 arcs have shown that demixing effect changes the chemical composition of the plasma. This effect. which is due to diffusion and to the difference between the ionization potential of fluorine and that of sulphur, leads to a depletion of sulphur near the axis. So in this region, the ratio M (called the demixing factor) between the fluorine concentration (atoms + ions) and the sulphur concentration is greater than 6 (6 being the stoichiometric value). On the other hand the usual modelling of these arcs is based on the hypothesis of the stoichiometric equilibrium coupled with LTE assumption. In this communication we present first the calculation of the material functions (transport coefficients and radiation losses) of S + F plasma for different values of the M factor, and second, the calculation of the temperature in these kinds of mixture, in order to study the influence of demixing on the axis temperature of SF6 wall stabilized arcs